Strukturelle Thermodynamik des Hochtemperatursupraleiters ErBa$_{2}$Cu$_{3}$O$_{6+x}$

Pörschke, E.

Book/Report

FZJ-2018-03319

Strukturelle Thermodynamik des Hochtemperatursupraleiters ErBa$_{2}$Cu$_{3}$O$_{6+x}$

Pörschke, E. (Corresponding author)FZJ*

1990
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Berichte des Forschungszentrums Jülich 2386, 101 p. (1990)

Please use a persistent id in citations: http://hdl.handle.net/2128/18799

Report No.: Juel-2386

Abstract: Pressure-composition-isotherms for the solution of oxygen in ErBa$_{2}$Cu$_{3}$O$_{6+x}$ were measured in the pressure range between 10$^{-1}$ mbar and 10$^{4}$ mbar and at temperatures between 450 °C and 750 °C. The results were used to derive the relative chemical potential, $\Delta \mu$o, the relative partial molar enthalpy, $\Delta$Ho, and entropy, $\Delta$So, of oxygen. In addition, the location of the orthorhombic-to-tetragonal phase boundary was determined by resistivity measurements between 480 °C and 650 °C. Structural parameters of a series of ErBa$_{2}$Cu$_{3}$O$_{6+x}$ samples with concentrations of 0 $\le$ x $\le$ 1 were obtained by X-ray and neutron scattering. The transition temperatures to superconductivity, T$_{c}$, were determined by susceptibility measurements . The experimental results provide the basis for a discussion of the relations between structural changes and the transition from superconducting to nonsuperconducting behaviour of ErBa$_{2}$Cu$_{3}$O$_{6+x}$ with varying $\chi$. The measured $\Delta \mu_{o}$-, $\Delta$H$_{o}$- and $\Delta$S$_{o}$-curves are used to test two-dimensional lattice gas models for a solution of oxygen in ErBa$_{2}$Cu$_{3}$O$_{6+x}$ proposed in the literature.The basic results are the following: 1. ErBa$_{2}$Cu$_{3}$O$_{6+x}$ samples that are orthorhombic at room temperature are not necessarily superconducting. 2. The change from superconducting to nonsuperconducting behaviour coincides with a change in the relative position of oxygen between the CuO chains and CuO$_{2}$ planes. This observation supports the model of a charge transfer between planes and chains explaining the loss of superconductivity with decreasing oxygen concentration. 3. The relative partial molar enthalpy, $\Delta$H$_{o}$, depends only slightly on oxygen concentration. At $\chi$ = 0 one gets $\Delta$H$^{0}_{o}$= -83 kJ mol$^{-1}_{o}$ and $\Delta$S$^{0}_{o}$= -75 J mol$^{-1}_{o}$ K$^{-1}$. At the phase transition from tetragonal to orthorhombic, $\Delta$H$_{o}$ decreases by 5.5 kJ mol$^{-1}_{o}$ and $\Delta$S$_{o}$ by 6.5 J mol$^{-1}_{o}$ K$^{-1}$. 4. Two-dimensional lattice gas models may describe qualitatively the oxygen solution in ErBa$_{2}$Cu$_{3}$O$_{6+x}$. However, neither models using only nearest neighbour interactions, nor those using nearest and next nearest neighbour interactions, yield a quantitative description as shown by calculations using analytical approximations and Monte Carlo simulations.

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